The use of interconnecting pipe, particularly plastic pipe, is becoming more common in industrial and commercial settings. As a result, there is an ever increasing demand for speed and ease of installation while retaining leak-proof seals and providing a joint that will not separate during installation or from hydraulic pressure within the pipe, thus preventing spills of environmentally hazardous substances, product, or other materials being carried through the interconnected pipes.
Early designs utilized a sleeve assembly which fits over the outside of the two pipe ends to be joined. An example of this prior art is found in the Magnani patent, U.S. Pat. No 2,829,909, which utilized an external sleeve and a plurality of O-rings retained within grooves in the inner wall of the sleeve. These O-rings provided the seal for the joint and the frictional resistance to retain the pipe ends joined together within the external sleeve. This design, however, did not provide a positive locking mechanism to securely retain the two pipe ends within the sleeve.
Another example of a sleeve fitting is found in the Mitchell patent, U.S. Pat. No. 4,130,302, which also utilizes an O-ring configuration within pressure chambers that provides the seal within the sleeve. A crimp is made in the sleeve once the pipe ends are inserted to aid in retention of said pipe within the sleeve.
Other pipe joint assembly techniques utilize an external sleeve with a retention groove circumferentially cut into the connecting ends of the pipe. The inserted pipes are then retained within the connecting joint by means of a ring assembly or nylon splines. The Carstensen patent, U.S. Pat. No. 5,584,512, is an example of a pipe connection fitting whereby the seal is located at the point where the two connecting pipes meet, and the retention means consists of increasingly wider snap rings contained within the inner diameter of the sleeve which drop into place in matching width grooves contained in the outer diameter of the spigot end upon insertion within the sleeve.
Similarly, CertainTeed Corporation markets plastic pipe utilizing a sleeved joint connection assembly wherein the connecting pipes are inserted into the sleeve until contacting a positive stop. A circumferential groove is cut within the inner diameter of the sleeve on each side in proximity to the positive stop into which a rubberized ring gasket is placed so as to seal the joint. Located outwardly from this groove, a spline groove is cut circumferentially in the inner diameter of the sleeve. A corresponding matching spline groove is located in the outer diameter of the inserting pipe into which a nylon spline is inserted which is sufficiently stiff so as to act in concert with the matching spline grooves to prevent the joined pipes from pulling apart.
With the locking joint available from CertainTeed Corporation, the worker must thread nylon splines through the matching spline groove opening at each end of the sleeve adding to the number of parts necessary to be handled and the time associated with installation of the interconnected pipe.
The current invention can use a sleeve assembly such as has been used in the past, but also is designed for use in pipe having a bell end which receives the corresponding spigot end of the pipe so as to create the sealed lock joint. The ease and speed of assembly and the diminished number of parts necessary for the assembly process are evident.
A more significant problem associated with sealing lock joints holding interconnected pipe concerns the grooves circumferentially cut into the outer diameter of the pipe wall in conjunction with the sleeve assembly or other connecting apparatus.
In both the Carstensen U.S. Pat. No. 5,584,512, and the system offered for sale by CertainTeed Corporation, receiving grooves are circumferentially cut in the outer diameter of the pipe to be connected. This creates a point of weakness by reducing the minimum wall thickness of the pipe at that locale. As a result, some pipes that claim to meet minimum wall thickness specifications for projects are in actuality under-dimensioned resulting in rejection of the installation by Engineers. In order to overcome this dimensional deficiency pipe having a greater thickness may be utilized which, when the circumferential groove is cut, will maintain the minimum wall thickness required by the specification of the project. This, however, adds significantly to the expense of the pipe to be utilized on the project.
The reason for increasing concern and rejection of pipe connection systems wherein the circumferential groove cut in the outer diameter of the connecting pipe is the location of the groove in relation to the seals. In the above cited references, the circumferential groove in the outer diameter of the connecting pipe is cut on the pressure side of the pipe. In other words, as a result of the location of the retention groove in conjunction with the seal of the joint, the inner wall of the pipe immediately opposite the groove cut in the outer diameter is carrying the full pressure of the liquid or other material being retained within and carried through the pipe. By reducing the minimum wall thickness at this locale, the pipe is weakened and presents the opportunity for cracks or fractures developing with the ultimate leakage of material out of the pipe.
The current invention addresses this concern by locating the circumferential groove cut in the outer diameter of the inserting end of the pipe inside of the sealing gasket. As a result, the inner wall of the inserting pipe at the locale corresponding to the circumferential groove is not required to carry the pressure of the material contained therein. This pressure is carried by the pipe wall comprising the bell end or sleeve of the receiving pipe into which no groove has been cut so that minimal wall thickness requirements are maintained thereby enhancing the strength and durability of the pipe at the point of connection.
It is evident to those skilled in the art that this invention may be used on a wide range of pipe diameters and is particularly useful in the interconnection of PVC pipe. It is further useful for the interconnection of other plastic pipe, metallic pipe and piping made of other materials.